The world market for sparkling and gassy wines is in full expansion and already exceeds two billion bottles per year produced in more than 50 countries. One of the essential aspects, which is of crucial importance, is the correct and safe sealing of this type of bottle.
In fact, in the case of champagne and sparkling or gassy wine, the sealant has to guarantee the seal in such a way as ensure that pressure inside the bottle is maintained. For sparkling wines the pressure inside the bottle is in excess of 1.5 bar.
The demands of the sparkling wines market are many and specific, with the most important of them being; the homogeneity of performance (sealing, ageing, behaviour after being opened and preservation of the organoleptic characteristics), acceptance by the market (traditional appearance of the cork in the shape of a mushroom) and high quality in relation to cost.
The market currently prefers the use of cork sealants and these now account for 80% of that, with the remaining 20% taken up by synthetic sealants and screwcaps.
The cork sealants currently used can not meet all the demand.
Cork agglomerate stoppers are currently produced by two distinct processes:                By continuous reactive extrusion, also known as the “extrusion process”        By compacting-reaction in a closed mould, also known as “individual moulding process”.        
In the first of these processes, the granulated cork, previously moistened with the prepolymer additive is continuously compressed through a heated tubular segment. Compacting induces the filling in of the spaces between the granules with prepolymer additive, which under temperature polymerises the edges of the agglomerated granulation. The continuous cylindrical rod produced in this way is subsequently sectioned off into pieces of suitable length. After the finishing operations have been applied, a stopper with the required length and diameter is obtained.
In the second of these processes, the granulated cork, having been previously moistened by the prepolymer additive, is fed in a semi-continuous way into the cylindrical moulds. The granulation is then compacted in the moulds by two cylindrical pistons. The pressure applied for several minutes in the hot mould allows polymerisation reaction to reach a high level of transformation, typically more than 95%, and so reduces dilatation following removal from the mould.
There are two other processes which are not described as they are considered to be irrelevant; namely tubular centrifuged agglomerate and paralellepipedic blocks.
The agglomerated stoppers with a diameter of between 25 mm and 30.5 mm are the result of the agglomeration of cork granules (measuring between 2 and 8 mm) and of a combination of chemical additives by means of an extrusion process, used, to take an example, in the process registered in the British patent GB 517798 or, less frequently, in the individual moulding process.
The quality of these stoppers is generally considered to be inferior to that desired, due to either the manufacturing process or to the raw materials chosen, in response to the pressures of competition.
Using these stoppers can lead to random ageing of the organoleptic characteristics of the wines, and also to unreliable behaviour in preserving the CO2.
The stoppers which are used most to seal bottles of gassy or sparkling wines are those consisting of a cylinder of agglomerated cork, with two discs of natural cork bonded onto each of the ends.
The agglomerated cylinders are obtained by agglomeration of cork granulates with the average sizes of the granules of between 2 and 8 mm, together with chemical additives, and by means of a reactive extrusion process or by moulding.
The cork discs can therefore be used in the traditional manner or as described in the patent EP 0481155. Bonding by gluing two materials with different physical characteristics whereby one of them undergoes intrinsic variability and heterogeneity of a natural material, and which leads to a not entirely satisfactory homogeneity of behaviour.
The “new generation” agglomerate corks are obtained by agglomeration of cork granulation through a moulding process, and have a minimum weight of 51 percent of granulated cork, with a granulometric measure of between 0.25 and 8 mm, and more frequently between 0.25 and 2.5 mm.
These stoppers are prepared by processes which aim to improve organoleptic neutrality of ageing and may contain expandable synthetic materials as described in European patent EP 0496687. In accordance with the processes used, these stoppers can probably fulfil the usage requirements, namely in regard to homogeneity of mechanical and organoleptic behaviour. However, the visual aspects of the cork, in general, do not meet the expectations of potential customers.
Spanish Patent ES2160005 (Martin) describes an agglomerate stopper with or without glued cork discs and a wire frame. There is only one type of agglomerate, and in this case the cork discs are glued and not bonded closely during moulding (the bonding surface is regular). Neither the preparation process is described nor claimed.
Spanish Utility Model ES1043200 (Emporda) describes a stopper formed of three separate parts: The first is of rough agglomerate (4 to 8 mm), the second of natural cork and the third of fine agglomerate (20.5 to 3 mm). The agglomerate parts are obtained separately by extrusion in unit moulds or in blocks. The parts are glued and not closely bonded during moulding (the bonding surface is regular).
Spanish Utility Model ES1047917 (Emporda) is similar to the Spanish Utility Model ES1043200 and also describes a stopper formed of three separate parts: The first is of rough agglomerate or with impermeabilising agent, the second is of natural cork and the third of fine agglomerate with impermeabilising agent. The parts are glued and not closely bonded during moulding (the bonding surface is regular). The preparation process is not described.
Spanish Utility Model ES1057788 (Rutllant) describes a stopper formed of two or three separate parts: The first is of rough agglomerate (2.72 to 4.75 mm), the second is of fine agglomerate (<1 mm) and the third, if there is one, is of natural cork. The parts are glued and not closely bonded during moulding (the bonding surface is regular). The preparation process is not described.
Spanish Utility Model (Trefinos) describes a stopper formed of an inner cylindrical core of rough agglomerate (3.5 mm) and an outer ring of fine agglomerate (0.5 mm). This product is obtained by extrusion, based on two concentric draw frames.
Spanish Patent ES2255389 (Janosa) describes a stopper consisting of fine agglomerate and a disc of natural cork. The process of fabricating this stopper is by a mixture of the components of the agglomerate and incorporates the disc of cork during the moulding. However the stopper does not have rough agglomerate and has a cork disc, with the bonding surface being regular. The process uses just one mixer.
German Utility Model DE 201 19 241 U1 and German Patent 1936646 describe stoppers which consist of two parts of natural cork separated by a impermeabilising disc of plastic material.
Patent Request WO 2006/003284 describes stoppers of agglomerate cork of just one type with two discs of natural cork glued to the same face of the agglomerate, with the bonding surface being regular, as well as the process of fabrication.
French Patent Request 2 838 714 describes stoppers for sparkling wines of agglomerate cork of just one type, which also has a glued disc of natural cork, with the bonding surface being regular.